Manufacture of zinc oxide



Jan, 6, 1925.

F. G. BREYER ET AL MANUFACTURE or ZINC OXIDE Filed May 27, 1922 5 Sheets-Sheet 1 2%??? 2213M WWW/M PM Bum; W 7W Jan. W25. 1,522,097

F. G. BREYER ET AL MANUFACTURE OF ZINC OXIDE Filed May 2 1922 5 Sheets-Sheet 2.

amoemtoz F. e. BREYER'ET AL MANUFACTURE OF ZINC OXIDE I Filed May 2'7, 1922 5 Sheets-Sheet 5 F. G. BREYER ET AL MANUFACTURE OF ZINC OXIDE ,Filed May 27, 1922 5 Sheets-Sheet 4 Jan. 6, 1925.

IN VENTORS rdfifi' 5 Sheets-Shet 5 Filed May 27, 1922 INVENTORS I BY 5M4 c Patented J 6, 1925.

UNITED STA TES PATENT-OFFICE.

FRANK G.BREYER, EARL C. GAS KI I LL, AND JAM'ESA. SINGMASTER, OF PALMERTON,

IPENNSYLVANIA, ASSIGNORS TO THE NEW JERSEY ZINC COMPANY, 01 NEW YORK, N. Y.. A CORPORATION OF NEW JERSEY. I 4

MANUFACTURE OF zinc OXIDE.

Application filed May 27, 1922. Serial No. 564,021.

To all whom it may concern:

Be it known that we, FRANK G. BREYER, EARL C. GASKILL, and JAMES A. SING- MASTER, citizens of the United States, residing at Palmerton, county of Carbon, State of Pennsylvania, have invented, certain new and useful Improvements in the Manufacture of Zinc Oxide; and we do hereby declare the following to be a full, clear, and

exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use. the same.-

This invention relates to the manufacture of zinc oxide, and has for its object the provision of an improved method of manufacturing zinc oxide.

llcretoforc, zinc oxide has been generally produced by either the American (or V Vethcrill) process or by the French (or retort volatilizing) process. the zinc oxide used in the rubberindustry as a reinforcing agent has been heretofore manufactured by the American process. In

the production of zinc oxide by theAmerican process, a charge of zinciferous material mixed with a reducing agent and spread. onan ignited bed of fuel is subjected to a combustion supporting blast or draft and broughtto a sufficiently high temperature to reducethe compounds of zinc and volatilize the reduce metal, the zinc vafpors burning in drifting or rolling flames above the top of the charge and in the off-take pipes or flues to zinc oxide, whichis'col- 'lected in an appropriatmmannen In the French process of producing zinc oxide,

metallic zinc is melted and volatilized in appropriate receptacles oi retorts, under non-oxidizing conditions, and .the resulting metallic zine vapor drifts or flows out of the mouth of the retort at low'velocit-y and burns in the air with a quiet, rolling or drifting flame, thereby forming the zinc oxide which is collected in an appropriate manner. In these and other processes heretofore proposed, there has been no appreciation of the fact that the nature of the'flame it.

' self has any influence on the physical properties of the oxide, nor has any attempt The great bulk' of particles are ofta size within the range of I photomicrographic measurment with glass lenses and White light. l i I Our improved method df producing zinc oxide involves directing a blast of relatively cool oxidizing gas, such as air, against an issuing stream of metallic zinc vapor. We

have discovered that azinc oxide product'of 1 greatly improved properties and of "extreme and ultramicroscopic, fineness can be' produjced by oxidizing an issuing stream of me:

tallic zinc vapor by alblast of relatively cool oxidizing gas, such as air, Where the gaseous blast'restricts the zinc-oxide-torming area envelopingthe issuing stream of zinc vaporand absorbs the heat generated in the zincoxide-forming area, thereby lowering the temperatureof the combustion or oxidizing zone and 'coolingthe resulting very fine particles of zinc oxide substantially in-. I

stantaneously after their formation. The

oxidation by blasting of the issuing stream of zinc vapor preferably takes place in the open, or in an enviroment wh ch permits such complete dissipation or absorption of the radiant energy of the oxidation as to substantially assist the blast in'producmg and maintaining a restricted and relatively;

" cool combustion zone. -Thus, the oxidation eo'usly take place by blastin may advanta a if heat-reflectin in a large open room, an

objects are in' proximntytto the zoneo oxidation such objects should p at 'so' low a temperaturethattheyabsorb rather than reflect the radiant energy. of the oxidation.

Preferablyfthe volume; andlintensit the gaseous blast and ts heat-absor ing capacity are such'that the part1clesof zinc oxide are cooled below a temperature'of 350 C. in avvery small fraction of a second, sayin'one twenty-fifth (1/25) of a second,

lleimaintained o illustrated certain forms tensifying and -concentrating or less, after their formation. In our preferred practice, the volume, intensity and heat-absorbing capacity of the gaseous blast are such that the apparently white hot zone of combustion or oxidation is in reality so restricted and cool that the bare human-hand may be passed back and forth through the combustion zone with impunity, Where the issulng stream of zinc vapor is approximately the equivalent of 150 pounds of zinc issuing per hour from a nozzle 1 inches in diameter. The stream of zinc vapor may be either undiluted or other gases such as carbon monoxide, nitro-. gen, hydrogen, etc., resulting from the method used in producing the zinc vapor.

In the accompanying drawings we have of apparatus (in diluted by a similar intensive rotation, brings about chilling and dilu- The crucible is divided into two compartments 12 and 13 by means of a transverse Figs. 1 and 3 to 7) adapted for the practice of the process of the invention, but it is in' tended and will beunderstood that the in- 'vention is illustrated by, but is not limited to, the use of the particular forms of apparatus thus illustrated and described.

In the accompanying drawings.-

Fig. 1 is a sectional elevation, somewhat diagrammatic in its character, of a suitable form of apparatus for the process of the invention; I

Fig. 2 is an explanatory view of a freely burning flame of metallic zinc vapor, burning in air in accordance with-normal French process practice of the prior art;

Figs. 3, 4, 5, 6 and 7 illustrate certain modified arrangements of apparatus, similar to parts of Fig. 1, for intensifying the compractice of the bustion of thezinc vapor and instantane;

'ously chilling and diluting the resulting fume; Figs. sion machine for testing vulcanized rubber products containing the new fume product; Fig. 8 being a plan, Fig. 9 a vertical section (with parts omitted), Figs. 10 and 11 being respectively plan and vertical section of the holder for .the rubber samples, Fig? 8 to 14 inclusive show an abra- 12 being an enlarged view showing the test specimen in place in" the holder and Figs. 13" and 14 being enlarged views of one of the brushes'and one of the vacuum chambers respectively;

In the apparatus of Figs.'1and 3 to 7 various arrangements are shown for inthe "combustion 'within limited dimensions and for producing a relatit ely cool combustion zone, so

- that the particles of zinc oxide are formed very fine. and will be instantly strong blastso'r drafts of air.

removed from the region of even slightly elevated temperature prevailing in that zone, the particles being blown throughand out of the intensive combustion zone by It will be understood, however, that other and equivalent meanscan be similarly used, such as a rotating nozzle' or orifice which, by its chilled and 1 shown) are provided for regulating 19,'and

' suitablewallor partition 14. The lower endof the partition 14 isspaced a short distance from the adjacent wall of the crucible and in,

this space is arranged a perforated diaphragm15.

The crucible 10 is enclosed by a brick structure 16 and the space between the brick 'work and the inclined walls of the crucible may, if desired, be filled with ,heatinsulating material 17, such as sil-o-cel. The com pa'rtment 12 of the crucible is permanently closed by a cover 18 supporting an appropriate depth of heat insulating material 19.

The compartment 13'is normally closed by a removable cover 20.

An electrode-21, preferably of graphite, extends down along the partition 14 well beneath the surface of the zinc in the compartment 12. Another electrode 22, also preferably of graphite, extends into the compartment 12 and terminates at its lower end ashort distance abovethe level of the zinc. The electrodes 21 and 2&2 arefconnected to an appropriate source of electric energy, which may be either direct or alterirating, and -,appropriate means (not electric current.

A nozzle 23 extends through the cover 18 terial 19, and for the metallic zinc compartment 12.

Mounted on top of the insulating material cula-r compartment24 which' is adapted to be supplied with compressedair from any source through the supply pipe 25. The compartment 24 has an annular orifice 26 surrounding the nozzle 23 and discharging upwardly into the escaping stream of metallic zinc Vapor. 'llhe outer annular .wall of theqompartment: 2% may be of fire brick and the top cover plate of the compartment may be of steel. The cone 27 mav. be iof sheetiron-and may have an insulat ing material," such as sil-o-cel, packed between it and the nozzle 23.

In the practice of the process of the inand superposed layer of insulating ma-i provides a discharge outlet vapor produced in the a 1115 surrounding the nozzle 23, isa cirvap vention with the apparatusv illustrated in Fig. 1, metallic zinc is introduced into the crucible until the compartment 12 is filled to about the level indicated with molten zinc, and this approximate level is "mamtained in the normal operation of theapparatus. rent between the electrode 22 and the surface of the zinc 11 develops sufficient heat to maintain the zinc in a molten condition and to produce sufiicient metallic zinc vapor so that a rapid stream of the vapor will escape through the nozzle 23. The heat is also sufficient to meltadditions of solid zinc, partment 13 by removing the cover 20,

The space between the top surface of the molten zinc in the compartment 12 and the cover 18 becomes filled with metallic zinc vapor and this vapor passes through the nozzle 23 in a steady stream.

As the zinc vapor issues from the nozzle,

23 it comes in contact with the surrounding air and if uninfluenced would burn with the characteristic naturalzinc flame.

circumferential blast or draft of air inwardly against the escaping stream of zinc or and causes its intense combustion. The effect of this air blast is to radically reduce the size of the zinc flame from the size which it would normally have if burning freely in the air without the added blast. The annular air blast has the further effect of lowering the temperature of the combustion zone and instantly chilling and removing the initially very fine particles of zinc oxide from the region of even slightly elevated temperature prevailing in the combustion zone. The zinc oxide particles thus formed are drawn into the lower flared end of a flue 29 by means of a suction fan or the like (not shown) in the flue system, and

are conveyed through the flue system to a bag house or to other appropriate means for the collection of the zinc oxide.

The effect which is produced by the'air blast in intensifying or concentrating the combustion of the zinc vapor will be evident from a. comparison of the intensive combustion zone and the ordinary free-burning zinc flame shown in a somewhat conventional and illustrative manner in Fig. 1 and Fig. 2, respectively. It is difiicult to illustrate graphically the difference between this intensive combustion zone and the freeburning zinc flame, but the visual difference is most marked. In Fig. 2 we have illustrated what we now believe to be the conditions attending the free burning in air of a. stream of substantial size of zinc vapor, for example, a stream escaping through a nozzle four inches in diameter and at a rate of one hundred and fifty pounds of metallic zinc passing through the The passage of the electric curwhich may be introduced to the com-- The vannular nozzle 26 directs an annular or such temperature,

turned ofi'. When, however,

ately intensified and mediately changes several feet in height to tion zone which is only some inches in is assumed to. be discharged upwardly from the vertical orifice or nozzle a. 'A core of.

metallic zinc vapor b forms above the orifice a. The core I; of zinc vapor is surrounded by air and the burning of the zinc vapor apparently takes place mainlyon the outside of the core where the zinc vapor strikes the surrounding air, and this active combustion zone, indicated at c, is the zone of highest temperature. To the extent that the com.- bustion of the zinc vapor may be incomplete in the zone a, this zone may be enlarged, and may be of an irregular and eddying character as furtheramounts of. air mix with the partly burned zinc vapor, thus forming a rolling or drifting flame. the active combustion zone 0 is a suspend'e mass of solid zinc oxide particles The burning zinc flame creates a draft of air in the direction indicated by the arrows. d, and this inspirated air draft tends to cause the particles of zinc oxide to hug the flame, so that some particles of the zinc oxide, and more particularly those formed at the base of the flame, may be exposed to the action of the flame for an appreciable period of time as they risev upwardly in or in close proximity to the high temperature zone of combustion. In vpractice, a free burning flame of the character referred to will have.

The metallic zinc vapor. I l

Surrounding Y to the slow cooling of the incandescent particles of zinc oxide as they rise upwardly in admixture with the highly heated gases, is of considerable size, and the particles of zinc oxide are maintained at an incandescent temperature, or a considerable part of the zinc oxide/particles are maintained at so that the particles of the zinc oxide produced have a radically greater particle size than the improved product made in accordance with the present invention.

A flame of the character illustrated in Fig. 2 is produced if the airblast of Fig. -1 1s the air blast the combustion zone is immediconcentrated, and imfrom a flame which is is turned on,

height, and the particles of zinc oxideaproduced, instead of rising slowly and being maintained at an elevated temperature for an appreciable period of substantially instantly .Fig. 1, we; have secured excellent results conditions: The approximately .2001

under the followin crucible 10 containe for an appreciable time,

an intense combustime,-are removed. I from the zone'of 1ntense combustion and chilled and diluted very small fraction of a second.

- found. the arrangement of Fig.

-per minute at a pounds of molten zinc. The heatiiigdf the zinc was. effected with an electric ciirrent of about 3,000 amperes, with an alternating potential across the electrodes '21fand 22 of 5 about 30 volts. The nozzle 233was four inches in diam eter and about 150 pounds of metallic zinc. were distilled off and passed end of the fume pipe 29 was ten feet in diameter and was mountedtwo feet above the discharge end of the nozzle 23. EI'he temperature of the gases entering the lower end of the pipe 29v varied from about 60 C. near the'middle to about C. at the periphery. The velocit in the combustion zone was upwards of v the" total height of the combustion zone, althoiigh it varied somewhat and was of an irregular character, was considerably less than a foot on the average, so that the particles of zinc oxide are formed and escape from the intensive combustion zone within a The cool ing effect of an air'blast of the .describedis, in fact so great that the hand I can be passed back and forth through the 0 upper portion of hat appears to be the combustion zone "without injury. This upper part of the apparent combustion zone apparently contains still incandescent particles of zinc oxide diluted by 'cool air and 5 undergoing rapid chilling, so that the ap parent combustion zone or zone of incandescence extends. somewhat beyond the highthat the partlcles of zinc oxide formed are temperature zone of intensive combustion.

Insteadof usingan annular air blast of.

low pressure air inthe manner illustrated in Fig. 1, other arrangements of air blasts can be similarly used, although we have 1 to "give very satisfactory results, Figs. 3 to 7 inelusive, illustrate other forms of apparatus I v which we have found satisfactory, although We regard them as less advantageous than the arrangement of Fig. 1.

In Fig. 3 a compressed air pipe 30 extends through the insulating material 19 and terminates in an upwardly'directed discharge orifice 31 arranged inthe center ofithe nozzle We have obtained satisfactory results by blowing pressure of about'twenty pounds through a one-eighth inch discharge orifice, the other conditions being substantially the same as in'the particular example hereinbefore described. There is a tendency for zinc oxide to form around and close the discharge orifice 31 and precaution should be taken to prevent this, such as scraping away the zinc oxide from time to time.

In the arrangement illustrated in Fig. 4 two ,1 air pipes 33 are arranged on diafty feet per second character from five to ten cubic feet of air.

stream 0 zinc vapor and are supplied with air through pipe 32. These nozzles cause a flattening or narrowing of the zinc come busting zone in one direction and the compressed air is supplied; through an annular pipe 36 to a series of discharge nozzles 37. Three nozzles are shown equally, spaced apart and directed at different levels toward the, stream of metallic zinc vapor issuing from the nozzle 23. More than three blasts of compressed air may be used. In

practice, we'have used as many as sixteen air blasts. uniformly distributed about the nozzle 23; but We have found-that entirely satisfactory results can be obtained with three air blasts arranged in the manner shown. 7 V In the arrangement illustrated in Fig. 7 an annular nozzle is provided somewhat similar to that of Fig. 1, having an air supply pipe 40 and anannular chamber. 39 with an annular orifice 38.

In the carrying out of the process with the modified structures illustrated in Figs. 3 to 7 the proper regulation of the air blast enables the combustion of the stream of zinc vapor to be intensified so that the zoneflof combustion is greatly concentrated, and so immediately diluted by an excess of air at a radically lower temperature and instantly chilled. That is, the fine particles ot zinc oxide initially formed are scattered or 'dispersed bythe air blast and are enveloped and diluted by the relatively co'ol blast which has a suificient heat absorbing capacity so that the particles are substantially instantl chilled, and so that any substantial growt or increase in the size of the initially formed particles is prevented.

Theapplication of the air blasts in the various ways illustrated, accordingly, exerts a dispersing or scattering action, as well as a diluting and chilling action, upon the initially formed particles, and this action is combined with the intensive and concentrated combustion of the'zinc vapor, so that both the combustion and the diluting and chilling are. completed substantially ina'length-WI ening or spreading out. of that zone infthe ion- . blast is decreased changes in the particles such as are characteristic of processes heretofore commercially employed in the manufacture of zinc oxide.

The intense-combustion which characterizes the process of our invention is not to be understood as implying combustion'at ex-' ceedingly high temperatures. We have .hereinused the word intensive to define the combustion at a high rate within a restricted space or volume. Thus, by intense. combustion, we mean the combustion or oxidation of. the zinc vapor at a high rate within a'restricted space or volume. In practicing the invention in accordance with, our pre-' ferred practice, the method adopted for pro-. ducing the intensive combustion, namely a blast of air, lowersxthe temperature in the restricted combustion zone. One indication that the blast is'wo'rking under our preferred conditions is the fact that the combustion zone has 'a bluish white appearance. As the from this optimum intensity, the combustion zone increases in volume and takes on an increasingly yellow 'tinge characteristic of the normal zinc flame and becomes very much hotter. The ab.- sence of this yellow tinge in zone may beused as a practical -working criterion of the 'optimumintensity of the blast. The limiting .factor 1n intensifying point longer oxidized. Thus, by

I prevented microns and of French rocess [zinc or restricting the combustion zone is the where. all of the zinc vapor is ,no increasing the blast of air it is'possibleto intensify the combustion zone to such an extent that ncreasing amounts of zinc vapor are from oxidizing by the extreme chilling effect ofthe blast; I

The fume product (zinc oxide), produced. in the manner hereinbefore described. is characterized by an extremely fine particle size, which distinguishes it from the present day standard hi h grades of zinc oxide produced by either the American or the French process. The best commercial grades of America process zincoxide whichwe have examined have an average-particle size of from 0.38 to about'0.52 microns (a micron is 0.001 millimeter) hile the'best commercial grades oxide which' We have examined have an average particlesize of from about 0.36 to about 0.44 microns.

The improved zinc oxide'product produced inaccordance with the practice ofthe present invention under favorable conditions has an average particle size of about 0.15 less. The significance of this radical reduction in the size of the particles, in the case of the new product, will be evident from a comparison of theapproxi mate number of particles per gram of the product. In the case of a zinc oxide, such French process. zinc oxide,

' ticle's.

' particles per gram particles increases to about 331 trillions.

7 number of particles per gram of zinc oxide,

- particle, for purposes the combustion .zinc oxide, is rendered difficult because 0 and because of the spheres and whose p fined what we mean there are approximately-"2.64: trillions of particles per gram; while with with'an average particles'ize'df 0.4; microns,- there are approximately 5.17 trillion -par-" Witha pro particlesize of 0.15 microns, the her of a product duct "having an ,a'vetago is about 95.22 trillions while witha product "having an f -averageparticle size of 0.1 microns, the number. of other words, the improved zinc oxideprodnot, produced in the manner hereinbefore described, with an average particle sizeot 015 or less, contains many'timestas many particles per unit weight asthe best commercial grades of American and French process oxides heretofore available.

When we refer to particle size, and to-the we mean the diameter of the'average particle, and we will define the diameter of of the present specification and appended claims, as the armonic'mean of the three cubical dimensions which is derived from measurements of these dimensions. 7 I

'The definitionand determination of particle size, in the case of products such as the extreme fineness, enormous number of particles which even a small amount of themxid'e contains. One may speak definitelyf the diameter of a sphere, and of the definite'particle size of a mass of spheres of u iform diameterqbut' in the case of zinc'oxid we are dealing with a material which isnot in the form of articles are not uniform, and hence the meaning '0 particle size is less definitc tha n in the case of uniform spheres, and wehave accordingly deby particle size in the present specification. v The numerical values of particle'siz'e The, diameter of the average particle) which we have given have been determined by photoperfectly the micrographing with blue light (with a' 2-' I millimeter homogeneous immersion apo-' chromatic lens of 1.3 numerical aperture an at a magnification of 1500 diameter) specimens properly dispersed in glycerln. These determinations have been made in accordance with the procedure described in the paper by Henry Green, Journal of the Franklin Institute, November, 1921,;pages 637-666. Owing, however, to the ultra m1- croscopic size of the particles of the zlnc oxide product produced in'the manner hereinbefore described, recourse must be had to the use of ultra violet light and quartz lenses in carrying out the photo-m crographic method of measurement. The use of ultraviolet light in micro-photographic article by Koehler and von Bohr, Zeitschrift able as a reinforcing or stren solid truck tires The new product enables oxide has been ma fuer Instrumentenkunde, volu1ne'24, pages 341-349. y

Owing to the extreme particle size which characterizes theimproved zinc oxide product produced .in the manner hereinbefore described, and the. radicallynncreasednumberof 'particlesjvhich a 'unit weight of the productcontains, the product can be used to advantage for various purposes. The new product is of particular value for use in compounding with rubber, and its use enables a radical improvement t9 be obtained in the resistance to abrasion of the rubber composition, while it also enables a marked increase-to be obtained in the tensile strength of the rubber, and we have also obtained an acceleration of the cure. f

Zinc oxide has long been used extensively in the rubber industry,"a'nd its use results in a'marked improvement in the resistance of the rubber to abrasion. Crude, unreinforced rubber, when cured with the proper amount of sulphur and accelerator, has a l w resistance to abrasive Wear, and is totally unsuited for use, for example, as a tire tread stock. a

WVhen, however, zinc oxide is compounded with rubber, a very satisfactor rubber compound from the standpoint o abrasive wear is obtained. A

The new zinc oxide product produced in the manner hereinbefore described is partiresistance to reinforcer, and its use enables a radically increased'resistance toabrasi've wear to be obtained, as well as higher .tensile strength. The new fume product is particularly valuhening agent in rubber stock which is to e used in the treads of pneumatictifes or in the body of a resistance to abrasive wear to be obtained approximating or evemexceeding one hundred per cent. more than with the best grades of zinc oxide heretofore industrially employed fori reinforcing rubber. i

As a standard of comparison, we will refer to the best grade of rubber reinforcing zinc oxide now manufactured as expanys [special grade Horsehead brand of [zinc oxide The Horseheadv brand of zinc oxide has been most extensivelyv used in the rubber industryfor many years and the special grade has been the accepted stand-. ard of uniforimityv in zinc oxide for rubber compounding over a number of years, This 6 for many years by the well-known American 01' Wetherill process from the unique franklinite ore of'the Franklin-mine in New Jersey. The propertiesan'd uniformity of this oxide are well recognized, and are referred to in standard authoritieson-pigments. This oxide has a Sharp crushed lump quartz, 1Q-14 mesh 3 3 "and molded into the desired form.

byball bearings 5.. independent of it are supports '6 to which .are pivoted the holders Tfor the rubber- -the manner ber stockrforming separate segments of the tread. This tire is then placed in actual use. and the relative rates' of wear of the several segments observed and measured. In,

order to'avoid the cost and to shorten-the time required for such actual service tests,

test methods of determining the relative abrasive resistance of compounded rubber haveibeen devised. One such test method consists in subjecting the several pieces of compounded rubber to .the abrasive action of a. revolving'sharp sand concrete track and comparing the relative volume losses after a redetermined time.

In or er that the method of determining resistance to abrasion (abrasion indices) may be understood, we have illustrated, in the accompanying drawings, a machine which we have found very satisfactory and which has been found to give comparative results closely approximating those obtained in actual use with automobile tires.

if y advantageous use as a rubber! The abrasion machine consists essentially of a revolving track of on side diameter about The surface of this track consists of concrete of the following compositibn by volume:

' Parts. Portland cement 1 This cbmposition'is moistened with water The cement content is only sufiicient to bind the particles together, and the track consists essentially of quartz particles. After about 24 hoursthe top layer. of quartz concrete ,track belng ppo by a rotatable iron plate 2 particles .are removed by abradingthe track with a (.rasfi or other suitable abrading material.

ln'Figs. 8 to 14 the rotatable eoncrete' track is indicated at 1, this new which is rotated through the central shaft 3 by means of gears 4-, operated by any suitable means; The rotating track-is supported Above the track and specimens. The specimens-8 are inserted in s' lop-The slot 9 sample is inserted illustrated in Fig.12. and are rec ' arranged as shown and a weight of 3" pounds,

' revolving Suction pipesll are are connected with a suction fan. These suction pipes keep the track free from rubber dust which abrades from the samples under test. Brushes 12 are arranged at an angle as shown and assist in keeping thetrack free from abraded rubber. The suction devices aifd is at an angle of 30.

,the brush both assist in keeping the track clean. 4 In order to be sure on this point, however, the track is stopped every 500 revolutions and thoroughly brushed off. The

brushes are supported-by pivoted arms 13 pivoted to supports 14!. The holder 7 has the length of the arm from the nearest edge of the holder to the bearing being 6 inches. The holder itself has a length'of 5 inches, a width of 3 inches. The rubber,

and a thickness of {i inches. specimen has a size of 2 inches by 5 inches by inch and is inserted in the holder so that its area of contact with the track will be 4 sq. in. The track rotates counterclockwise, as indicated by the arrow in i Fig. 12.

In the use of the abrasion machine, the compounded rubber specimens to'be abraded are held stationary with respect to the track, the arrangement being as illustrated in Fig. 12. The rubber specimen is held against the track by. the weight of the clamp, which is constant. The clamp is free to move vertically to take care of unevenness of the track. The track is rotated at such a speed (about 32 R. P. M.) that approximately 0.3 cu. in. of rubber are abraded for 1000 revolutions of the track from a sample of rubber stock compounded with the aforementioned special grade Horsehead brand zinc oxide in accordance with the following composition:

First latex pale crepe (washed and Grams.

dried) 920 Sulfur; l-lexamethylenetetramine 6 Zinc oxide a 1 ,260

The crude rubber is first treated on the mllhng rolls, and when appropriately broken down, the other ingredients of the r composition are worked therein. After this mixture has been appropriately worked on the milling rolls thoroughly .to' incorporate all of the ingredients uniformly'throughout the crude rubber, the resulting product is 'allowedto stand for an appropriate period of time, usually twenty-four hours or so,

and'is then put into a hydraulic press vulcanizer and vulcanized. The time of cure is 90 minutes ata temperature of 141 C. with a hydraulic pressure of 2000 pounds per 7 the same treatment,

The figures losses in weight of the specimens their respective specific gravities. volume loss of -a speclmen varies lnversely sq. in. in a press-having a ram diameter of 10 inches and betweenthe platens of 120 sq. in. After the rubber has been removed from the press for 24 hours it is tested for tensile and abrasion resistance qualities. c

In operating the abrasion machine, four rubber specimens are arranged with the holders equally spaced apart over the track, so that all four specimens are subjected to thus giving relative with the area of the rubber I values. .Byweighing the sample before and after abrasion and determining its specific gravity, the volume loss can be computed. for relative abrasion resistance of different rubber stocks, the abrasion machine above-described, have been found to check up very closely with the relative abrasion resistance of those same stocks when put on as segments of a vehicle tire and subjected to actual service wear. In

as determined on using the abrasion machine, the volume losses of the rubber spec mens are determined by the divided by Sincethe as its resistance to abrasive wear, it is customary to indicate the abrasive resistance as the reciprocal of the volume loss, and this practice hasbeen followed in the determination of the numerical figures for abrasion resistance given herein. For example; if the abrasion index of the standard test specimen is assigned an arbitrary value of 115, and'ifi the volume loss of the standard is 4.050 per 1000 revolutions and that "of the specimen to be compared is 6.265, then the abrasion index of the last mentioned test specimen will be Horsehead brand zinc oxide as now manufactured and of the composition above referred to, and the other containing anequal weight of the new fume product produced in the manner hereinbefore described,

the two compositions being properly cured 1 and the relative resistance to abrasion being determined in the manner above described.

The following tables indicate the results obtained with rubber compositions compounded as hereinbefore. described.v Determination No. '1 was madevwith a rubber composition'containing special grade Horsehead brand zinc oxide of the composition and properties hereinbefore referred to.

'Determination No. 2 was made with the new fume product;

precialply increased the 'rate o-fcure. It also gave a marked improvement in the reslst- 1 ance to heataging.

2 I he following tables further illustrate the Further comparative results are illustratedin the table which follows. The compo- The" first part of the table shows the results. obtained with thenew fume product. The second part of the table shows the results obtained with the Horsehead brand zine oxide hereinbefore re'ferredto.

' After 14 days 70 C. Load lbs/sq. in, Time of Tensile cure Per cent Abrasion 7 minutes gi i elongation. resistance. Tensile cent i coefl' 4011s. Strength elongation elong: elong.

Y lbs/sq. in.

30 3, 595 752 i 72 2,948 607 1.5 400 1, 045 :2 as: a: a 1:82 5 o New 75 4: 030 ass 191 3: 22s s 2. 9 705 11 600 90 3, 920 068 206 3, 212 555 3. 2 670 1, 475 105 3, 833 679 226 2, 443 491 3. 4 590 1, 470 22 a; 222 e r 12 i'SS Horsehead brand zinc 31413 642 92 2: 925 57s 1: 9 s93 11 410 oxide 3, 575 041 99 2, 747 530 2. 1 675 1, 480 3, 570 659 2, 768 563 2. 5 v 593 1, 858 3, 207 629 109 2, 280 489) 2. 7 672 1, 490

results obtained with the new productas compared with the results obtained with the special brand 'of Ho-rsehead oxide hereinbefore referred to as a standard of, com- 30 parison. The composition used in the first two comparative samples was made up of 920 parts of rubber, 55 parts ofsulfur, 1:260 parts of zinc oxideand one part of diphenyl guanidine as an accelerator. The second comparative-results Were obtained with acompound made of 920 parts of rubber, 55

parts of sulfur, 1035 parts of zinc oxide and 25 parts of thiocarbanilid.

After 14 days 70 0. Load lbs./s q.'in., Time of cure 33 3 Per cent Abrasion V minutes lbs ls g in elongation. resistance. Tensile cent 40#s. q. strength 91 ongati on 300% elong. 450% along.

1 1bs./sq.1n.

l I 45 2,503 654 95 1,693 601 402 1, 194 60 2, 640 644 43 1, 917 001 1. 4 568 j 1, 240 Horsehead brand zinc .75 2, 532. 625 59 2, 038 693 544 1,250 oxide 90 2, 798 654 70 2, 013 509 I. 7 586 1, 285 V.

63 I New m an 1 3,450 605 252 mm 34s 1, 2,155 105 3,430 610' 250 1,653 307 v1,050 2,040 I 120 3,210 coo, m 035 29a 928 1,885

a After 14 days 10 of Load lbs/sq. in.

Time of Tensile cure Per cent Abrasion minutes elongation. resistance. Tensile PM cent vulccoefl' 4 1' elongation 300% elong. 450% elong.

45' 2,910 619 .70 2,205 571 595 1,380 60 3,007 594 94 2,177 533 1.7 697 1,570 Horsehead brand zinc 75 3,233 601 109 1, 948 480 2.2 820 1,795 oxide 90 3, 225 599 120 1, 548 397 2. 6 742 1, 595 105 3, 017 578 123 1, 566 387 3. 0 840 1, 710 120 2, 858 555 132 1, 090 247 3. 4' 850 1, 730 30 3, 313 632 185 2, 863 544 2. 7 712 1, 920 45 3, 996 628 266 2, 785 503 4. 0 983 2, 230 60 3, 637 586 290 2, 355 417 4. 6 1, 242 2, 557 New fume product 75 3, 485 587 275 2, 147 363 1, 287 2, 525 90 3, 252 572 315 1, .996 342 1, 2, 395 105 3, 240 569 282 1, 416 239 1, 337 2, 465 120 2,850 i 567 257 1, 320 224 1,212 2,250 From the above tables it will be seen that sition's tested were made accordin to the l o u I I O the new fume product imparted to the vulfollowing formula: camzed composition a radically increased v A abrasion resistance amounting to around lrst latex P r p 9 .5 one hundred per cent increase. It will also p be seen that the new fume product gave a H l' y materially increased tensile strength and ap- A1110. Oxlde Time of cure Tensile Strength Per cent Abrasion After 14 days 70 0.

Load lbs/sq. in.

Vulc. coelf.

minutes elongation. resistance. Tensile 4m lbs/sq. in. 8 1. 33353,; 300% elong. 450% along. v it fit? 2%; 33 324 i it 233 if? a f? brand Zinc 15 21708 000 75 21326 539 213 037 11325 a at a e at at a: 45 31600 024 190 31003 546 11:11:11: 300 I 11050 60 3, e13 620 201 2, 325 422 4. a 1, 015 2, 075 New fume product 75 3,593 620 223 1,740 331 4.9 1,075 2,100- 00 3, 090 027 23s 1, 470 282 5. 1 970 2, 010 120 3,033 512 230 1,000 211 92a 1, 910

The marked improvement in the vulcanparently but slightly affected, outside of ized rubber products obtained with the new fume product of the present invention will be readily appreciated by rubber tee nologists. The improved results which the present invention enables to be obtained are not obtainable, insofar as we are aware, with any zinc oxide heretofore commercially available.

The use of the new fume product of our preferred practiceinvolves such a radical improvement over the zinc oxide compounding agents heretofore commercially employed that precautions should be taken to avoid over-vulcanization when it is used, e. g., by reducing the amount of sulphur or the time of vulcanization, etc.

When the new fume product is made in the manner hereinbefore described, by the vaporization of high grade zinc and the intensive combustion of the zinc vapor, with substantially instantaneous dilution and chilling of the resulting fume, the fume product is free or substantially free from impurities, such as chloride, sulphate, etc., and we attribute in part the radically. improved properties of the new product as a rubber reinforcing agent to the absence or substantial absence of such impurities.

The unique qualities of the product of our preferred practice, as described above, are strikingly illustrated by its behavior when compounded with plantation rubber in the absence of sulfur or any other compounding ingredient.

.After mixing the usual way on the rolls the compound wlll be seen -to act short and dry and have the oxide into the rubber a marked tendency to roughen on the surface, very-much like a stock that contains sulfur and too fiery an accelerator and that is scorching on the rolls, to use rubber mill language.

If a sample of the compound mixed as above and containing zinc oxide of the invention to 100 volumes of first latex pale crepe is suspendedin benzol the compound will not' dissolve to a milky suspension as is the moral action of unvulcanized zinc oxide compounds of the prior art, but the sample will remain apabout 20 volumes of.

may be attributing some swelling, and the benzol will stay fairly clear, resembling in this respect a compound that has been vulcanized or air cured.

No other pigment in couunercial use behaves like this and we are inclined to attribute some of the excellent properties of rubber compounds containing the oxide of the invention to this apparent affinity for rubber which has no parallel in the zinc oxidesmanufactured in accordance with the heretofore customary practices of the pr or I art or in any pigment to our knowledge.

As the result of our investigations and researches, we have determined that the aver-' age particle'size of a zinc oxide has a very considerable influence upon the properties of the oxide as a rubber reinforcing agent. It is our present opinion that the improved properties of the zinc oxide, made in accordance with our present invention, as a rubber reinforcing agent are prob bly due in large measure to its greater degree of subdivision or finer particle size.

ally demonstrated that the finer the particle size of a zinc oxide, the greater is its re-:

inforcing or stren thening power m rubber,

and inparticular its capacity for imparting to rubber resistance to abrasive wear.

While, in the light of the information derived from our resources and investigations,

power of the zinc oxlde to particle size we to simply one of cause ,anclnot to the cause tself.

In certain of the appended claims, we

We have actuthis improved property the manifestationsof a i I have definedour improved method of makingzinc oxide with respect to its applicawear. invention has been oxide.

the application of manufacturing zinc oxide irrespective of the Horsehead brand zinc oxide,

, stant removal and chilling instantly enveloped by th chilling of the initially zinc oxide, by directing the said stream.

. bility for producing a zinc oxide product particular use to which the resulting zinc oxide product is put. We have adopted, as a standard of comparison, the special grade whose present day qualit we have hereinbefore defined, because this 'is-the present-day recognized standard of high gradezinc oxide for rubber compounding. e claim:

LThe method of producing zinc oxide which. comprises burning zinc vapor a d subjecting the burning vapor to sud en 0 chilling by a blast of air.

' 2. 'T e method of'producing zinc 'oxide, which comprises burning zinc vapor and subjecting the zinc oxide particlesgformed to sudden chilling, the combustion. and cooling being intensified to cause substantially inof the initially formed particlesof zinc'oxide. I

3. The method of producing zinc oxide,

'which comprises burning zinc vapor and ,directing a chilling blast of air upon the urning vapor, whereby the initially formed particles of zinc oxide are substantially chilled;

4. The method of producing zinc oxide, which comprises vaporizing zinc and form-. in a flowing stream of zinc vapor, and e ecting the intensivecombustion of said stream and the substantially instantaneous a blast of air upon The method of producing zinc oxide,

which mg a flowing stream of zinc vapo and inenveloping the issuing e excess air and formed particles of comprises vaporizing zinc and formwhlch comprises directing. a blast of rela- 7. The method of producing zinc oxide which comprises directing a blast of relatively cool oxidizing gas against an issuing stream-of metallic vapor and thereby restricting the zinc-oxide-forining area enveloping the issuing stream of zinc vapor and cooling the resulting particles of zinc oxide substantially instantaneously after their formation.

their formation.

9. The method of producing zinc oxide which comprises directing a blastof relativelycool oxidizinggas against an issuing stream of metallic zinc vapor and thereby restricting the zinc-oxide-forming area enveloping the issuing stream of zinc vapor and cooling the resulting particles of zinc oxide below a temperature of 350 C. in

-a very'small fraction of a second after-their formation.

10. The method of producing zinc oxide which comprises directing a circumferential blast of relatively cool air against an issuing stream of metallic zinc vapor and thereby restricting the zi;-nc-oxide-forming area and cooling the resu ting particles of zinc oxide below a temperature of 350 C. in a very small fraction'of a second after their formation.

11. The method of producing zinc oxide which comprises directing a blast of relatively cool oxidizing gas against an issuing stream of metallic z'nc vapor, the volume and intensity of the gaseous blast and its heat-absorbing capacity being such that the apparently white hotzone of oxidation is so restricted and cool that the bare human hand can be the. oxidizing zone or flame with impunity where the issuing stream of zinc vapor is approximately the equivalent of 150 pounds of zinc issuing per hour from a nozzle 4 inches in diameter.

12. The method of producing zinc oxide particles of zincoxide substantially instantaneously after stream of zinc vapor passed back and forth through tively cool oxidizing gas against an issuing stream of metallic zinc vapor, the volume and intensity of the gaseous blast and its heat-absorbing-capacity being such that the height of the,flame of burning zinc vapor does not exceed one footon the average where the issuing stream of zinc vapor is approximately the equivalent of 150 pounds of zinc issuing per hour from a nozzlc4v inches in diameter.

'13. The method of producing zinc oxide tensifying the combustion and chilling of -the particles of oxide formed so that the time of combustion and chilling is less than about one-fiftieth of a second.

6. The method of producing zinc oxide, w ich comprises burning zinc vapor and subjecting the zinc oxide particles formed to. substantially instantaneous chillin the combustion and cooling being intensified to give a fume product with an average particle size not exceeding-about 0.15 micron.

, and intensity temperature of the resulting zinc tively cool'oxidizin'g gas against an issuing stream of metallic zinc vapor, the volume of the gaseous blast and its heat-absorbing capacity being such that the oxide laden fume at a distance not exceeding three feet from the issuing stream of zinc vapor is less than 100 C. where. the issuing stream, of zinc vapor is approximately the equivalent of 150 pounds of zinc issuing per hour from a nozzle 4 inches in diameter.

14. The method of producing-zinc oxide which comprises directing a blast of relatively cool oxidizing gas against an issuing stream of metallic zinc vapor, the volume and intensity of the' gaseous blast and its heat-absorbing capacity being such that the resulting zinc oxide product has an average particle size not exceeding 015 microns. 15. The method of producing zinc oxide which comprises directing a blast of relatively cool oxidizing gas against an issuing stream of metallic zincvapor, the volume and intensity of the gaseous blast and its heat-absorbing capacity being such resulting zinc oxide product has the capacity of imparting to compounded rubber an increased resistance to abrasion of about 100% or more as compared with special grade Horsehead brand zinc oxide.

16. The method of producing zinc oxide which comprises burning zinc vapor and subjecting the burning vapor to air of such volume, intensity and heat-ab-v sorbing capacity that the temperature of the resulting .zinc oxide laden fume at adisfeetfrom the burning tance not exceeding 3 zinc vapor is less than 100 C.

which' comprises "burning and subjecting the the equivalent of 150 jectirig .the' products rate of at least that the which comprises burning a blast oi 17. The method of producing zinc oxide a flowing. stream of metallic zinc vapor, burning zinc vapor to a blast of air of such volume, intensity and heat-absorbing ca- ,pacity' that the. resulting particles of zinc oxide are cooled substantially instantaneously after their formation where the flowina stream of zinc vapor is approximately pounds of zinc issuing per hour from a nozzle 4 inches in'diameter. 18. The method of producing zinc oxide which comprises burning-a flowing stream of metallic zinc vapor in the open, and subof combustion of the burning zir'ic vapor to sudden cooling by a blast of air directed 'a-gainstthe flowing stream of zinc vapor.

19. The method of producing zinc oxide which comprises burning in the. open a flowing stream 7 f metallic zinc vapor at the 150 pounds of zinc per hour and subjecting the products of combustion of theburning zinc vapor to the action of a chilling blast of air. j

20. The method of producing zinc oxide metalllc zinc vapor in the open and subjecting the products of combustion f the burningzincvapor to the action of a blast of cooling gas and thereby producing a zinc oxide product having the capacity of imparting to compounded rubber an increased resistance to abrasion of about or more ascompared with spev cial grade Horsehead brand zinc oxide. 1

FRANK G. BREYER. EARL. o. GASKILL. JAMES A. SINGMASTER. 

